Research Interest

Research in our group focuses on a number of facets of inorganic and organic materials chemistry. We rely on the synthesis and crystal structure determination methods, complemented by advanced optical, magnetic, and theoretical techniques, to establish pathways for achieving new properties that can be modified or finely tuned via the knowledge of structure-property relationships. Our main research directions are
(1) molecular and photomagnetism;
(2) magnetism of intermetallic compounds and nanoparticles;
(3) solution chemistry of polyphosphide clusters;
(4) gamma-ray detection by plastic scintillators.
Students who join our group get extensive training in inorganic and organic synthesis, solid-state chemistry, X-ray and neutron diffraction methods, magnetic measurements, X-ray absorption spectroscopy, electrochemistry and UV-Vis spectroscopy, and electronic structure calculations for molecules and solids at the DFT level of theory. Besides equipment available in our labs, we actively utilize major research instrumentation in the Department, as well as centralized national research facilities at Oak Ridge and Argonne National Labs.

1. Molecular Magnetism and Photomagnetism. Certain complexes of d4-d7 transition metals exhibit magnetic bistability, a transition between the low-spin and high-spin states commonly referred to as spin crossover (SCO). They represent great interest with regard to the development of new paradigms in molecular electronics and high-density data storage. Our group is exploring hybrid materials that combine such complexes with (a) conducting charge-transfer salts, (b) organic ferroelectrics, or (c) magnetically bistable organic systems. To achieve these goals, we use a combination of synthesis, crystal structure analysis, and magnetic measurements, as well as various spectroscopic techniques to create novel materials with magnetically bistable Fe(II) centers. On this NSF-funded project, the most important achievements are: (1) a discovery of a narrow band gap organic semiconductor that also exhibits light- and temperature-driven spin-state switching; (2) a comprehensive analysis of symmetry-breaking structural phase transition in SCO materials; (3) a discovery of light-induced radical trapping (LIRT), a novel photomagnetic effect that allows light-induced breaking of diamagnetic dimers of organic radicals into paramagnetic pairs of radicals (refs. 5, 7).

2. Discovery of New Permanent Magnets and Magnetic Refrigerants. Itinerant magnets represent a peculiar class of materials, whose magnetic behavior is strongly dependent on the nature of electronic structure in the vicinity of the Fermi level, which can be thought of as a HOMO level for solids. The magnetism of such compounds can be effectively tuned by controlling the electronic band structure of the solid. While such materials traditionally have been a focus of condensed matter physics, the fast-paced development of methods for electronic structure calculations and appearance of reliable user-friendly codes allow solid state chemists to become actively involved in this area of research. This trend has been reinforced by the recent discovery of FeAs-based superconductors, which caused a renewed interest to the ThCr2Si2 structure type in the condensed-matter community. Our research thus far has focused on elucidating correlations between the crystal and electronic structures and magnetic properties of RCo2Pn2 materials (R = rare earth; Pn = P, As) to achieve better understanding and control over the type and temperature of magnetic ordering in these systems. We are also interested in exploring ternary borides as potential materials to be used in magnetic refrigeration at room temperature. Summarized below are the most important achievements on this project (funded by the NSF Division of Materials Research: (1) a discovery of a large magnetocaloric effect in AlFe2B2; (2) a dramatic modification of magnetic properties of ACo2As2 (A = Eu, Ca) by physical and chemical compression or direct electron doping; (3) a synthetic pathway to the preparation of phase-pure samples and single crystal growth of RCo2As2 magnets (R = La, Ce, Pr, Nd).